1. Field of the Invention
The present invention relates generally to semiconductor pressure sensors, and specifically, to hermetic packaging of semiconductor pressure sensors.
2. Background Information
Today, most low-cost pressure sensor packages are designed to address clean gases and/or non-aggressive fluids. FIG. 1 is a prior-art molded leadframe pressure sensor package 1. The sensor package 1 includes a sensor die 2 that is attached to a housing 3 by a soft adhesive (e.g., RTV, epoxy, etc.), as shown by numeral 4. The sensor package housing 3 is generally made out of a pre-molded plastic and includes a metal leadframe 5 for providing interconnection to external circuitry. The topside 11 of the pressure sensor is typically coated with a silicone gel 6 for communicating pressure from external gaseous media. The package further includes a lid 7 having an opening 8 for directing external pressure to the sensor. The silicone gel 6 provides a minimal amount of protection from gaseous media for the sensor, wire interconnects, etc. In the case of an absolute pressure sensor, pressure is applied from the topside 11, whereas for gage or differential pressure sensing, a pressure port 10 is provided on the bottom side 12.
However, this sensor package 1 has several drawbacks. First, since the sensor die 2 is attached to the housing 3 with a soft die attach material, the applied pressures from the bottom side 12 of the sensor die is typically limited to less than 150 pounds per square inch (xe2x80x9cpsixe2x80x9d). Second, the topside 11 of the sensor only supports inert gaseous with pressures limited again to less than 150 psi. This is because the pressure media that is applied to the topside 11 of the sensor will penetrate the intermediary coating (e.g., the silicone gel or other type of coating), causing reliability issues such as failure of the sensor over time or explosion of the silicone gel after rapid pressure changes. Third, the only use of fluid media with the sensor includes exposure to the fluid media from the bottom side 12 of the sensor. However, adhesives, soft or hard, are not considered hermetic and, over time, moisture and corrosive gases will penetrate the interface, causing the electronics of the pressure sensor to fail.
FIG. 2 is a typical prior art sensor package 20 for high pressure and fluid media compatibility. This type of sensor package 20 includes a sensor die 21 which is placed in a stainless steel housing 22 with hermetic glass feed-through pins 23. The sensor die 21 has an integral glass or silicon constraint bottom 24 which provides a sealing cavity 25 therebetween for a vacuum reference and stress isolation from the housing. The die attach material is typically a soft epoxy such as RTV. A metal diaphragm 26 is welded to the stainless steel housing 22 and an inside cavity 27 formed therein is filled with oil to allow transfer of pressure to the sensor die 21. This configuration isolates the sensor die 21 from the fluid media. The use of the metal diaphragm is the primary packaging technique available today for more demanding applications, with variations in pressure and ability to apply most fluids to the sensor package. However, this type of package only generally addresses specific applications and is very expensive.
Accordingly, there is a long-felt need in the sensor industry for a low-cost, long-term reliable solution to address the problems associated with conventional pressure sensors.
The present invention is a hermetic media interface for a sensor package. The hermetic media interface is incorporated into a pressure sensor package for interfacing directly to fluid and/or gaseous media. The pressure sensor package includes a semiconductor die and a pressure port that are housed in a pre-molded plastic package. In one embodiment, a eutectic solder is coupled between the semiconductor die and a metal pressure port to solder the same to the semiconductor die. The semiconductor die may be optionally metallized. In an alternative embodiment, the pressure port is made from one or more plastic materials and the pressure port is attached to the semiconductor die with an adhesive. An integral stress-isolation region may be optionally incorporated on the semiconductor die.